The present invention concerns loudspeakers. More particularly, but not exclusively, this invention concerns a loudspeaker enclosure housing a decoupled drive unit for a loudspeaker enclosure.
A conventional moving coil loudspeaker cabinet 102 is shown in FIG. 1. This utilises a diaphragm 104 driven by a coil 106 reacting against a field produced by a magnet 108. The coil 106 vibrates the diaphragm 104 in sympathy with an applied electrical signal to create a sound. The out of phase sound emanating from the rear of the diaphragm 104 that would otherwise interfere with this sound is trapped inside the volume interior 110 of the cabinet 102. This volume 110 acts as an air spring that resists the motion of the diaphragm 104. To counteract this force the magnet 108 may be rigidly held by a chassis 114 which fixes the loudspeaker in the cabinet. The chassis 114 consists of legs or a perforated cone, allowing the diaphragm 104 to radiate sound into the cabinet 102. When designing a loudspeaker unit, consideration needs to be given not only to the effects that arise from the air spring effect of the volume 110, but also the forces arising from the acceleration and vibration of the diaphragm. This vibrational energy excites the magnet 108 in anti-phase to the diaphragm 104 and some of this vibrational energy will travel via the chassis 114 to the panels of the cabinet 102. The cabinet 102 will then act as a secondary sound source whose output is dependent on its own mass, stiffness and surface area. It is not practical to make the cabinet radiate as a rigid body, so resonances are common. This output is generally seen to be undesirable and many steps are taken to reduce it.
One such way of reducing the transmission of vibrational energy from the magnet to the cabinet is to decouple the magnet from the cabinet by means of a resilient mounting ring. Such a decoupled loudspeaker unit is shown in FIG. 2, which shows a cabinet 202, with a coil diaphragm 204, coil 206, magnet 208, interior volume 210 and chassis 214 much like the unit shown in FIG. 1. The resilient mounting ring 216 connects the chassis 214 to the cabinet 202 and therefore decouples the chassis 214, and therefore the magnet 208, from the cabinet 202. This solution works well if the internal volume 210 is very large relative to area of the diaphragm 204 or if the diaphragm 204 is not significantly affected by the stiffness of the air spring 210. Below midrange frequencies the stiffness of the air spring 210 is often significant. If the air spring's stiffness is significant, relative to the resilience of the mounting, then the magnet 208 will move in addition to or even in preference to the diaphragm 204, resulting in a loss of and/or distortion in acoustic output.
The present invention seeks to mitigate the above-mentioned problems. Alternatively or additionally, the present invention seeks to provide an improved loudspeaker enclosure.